The present invention relates to a perfected pumping device for feeding fuel from a tank to an internal combustion engine, and comprising a high-pressure pump and a low-pressure pump connected upstream from the high-pressure pump.
A pumping device of the above type is described, for example, in Italian Patent Application n. TO95A000010 filed on Jan. 10, 1995 (corresponding to U.S. Pat. No. 5,571,243), by the present Applicant, and is used as part of a fuel injection system also comprising an on-off valve, which, when idle, disconnects the two pumps, is opened by the fuel pressure of the low-pressure pump to supply the engine, and also provides for feeding the surplus fuel into an inner chamber of the high-pressure pump for lubrication and cooling purposes.
In the known device, the high-pressure pump is a piston type activated by the drive shaft; the low-pressure pump is activated by an electric motor; and the on-off valve is so sized as to supply the high-pressure pump and the inner chamber with the necessary amount of fuel as of the cranking stage. Operation of the electric motor powering the low-pressure pump, however, is generally unreliable, and, what is more, places added stress on the battery precisely at the cranking stage.
Replacing the electrically powered low-pressure pump with one activated by the drive shaft has so far been unfeasible, due to the low-pressure pump, at low engine speed at the cranking stage, being unable to supply enough fuel to open the on-off valve. On the other hand, sizing the on-off valve to enable it to be opened even under low fuel supply conditions would result in high steady-state fuel supply by the low-pressure pump, thus increasing the fuel pressure in the low-pressure circuit and so requiring a pressure regulator between the two pumps.